Field of the Invention
The present invention relates to power cylinders for imparting motion to objects and, more particularly, to a power cylinder which has three stable positions for effecting varying degrees of motion of objects which are connected to it.
Hydraulic mechanisms for moving various objects between a number of positions are old and well known. Frequently, they are used in multiples when it is desired to move two or more separate objects through differing lengths of travel.
In some instances, it may be desirable first to effect a limited motion of one object and then to effect concurrent movement of two objects. To achieve such results, it is frequently necessary to utilize a pair of mechanisms operated concurrently or in tandem to effect the desired motion of the individual objects. Providing dual mechanisms to effect concurrent motion of a pair of objects obviously requires duplication of the power assemblies and concomitant use of space as well as added power and control requirements.
In some structures, it is desirable to have inner and outer doors which are to be moved between open and closed positions, with one of those doors desirably being able to be moved into a partially open position when required. This may present problems when the doors o other operating elements to be moved by the power cylinder assemblies must act against substantial pressures or when the drive path to, or the location of, the objects being controlled provides only limited space for the power cylinder assemblies.